Gases, Transport & Thermodynamics

• Properties of gases and gas transport are explored in the provided material.
• Assoc. Prof. Mai Hong Hanh presented this information in 2022.

Outline of Topics

• The presentation covers the kinetic model of matter.
• Gas pressures and Boyle's law are explained.
• Measurement of gas pressures is described.
• Gas solubility in liquids is examined.
• Osmosis and Osmotic Pressure is noted as very important.
• Thermal properties of matter are discussed.
• Entropy is explained for specialists.

Learning Objectives

• Recognize thermodynamic systems and their surroundings.
• Define the Zeroth Law of thermodynamics.
• Thermal processes are analyzed in an ideal gas.
• Change in entropy is calculated in a thermodynamic process.
• Grasp of gas solubility and diffusion is targeted.
• Comprehend Osmosis and Osmotic pressure.
• Recognize transportation in membrane and the kidney.

Simple Kinetic Model of Matter

• Matter consists of molecules in continuous motion.
• Total internal energy includes kinetic and potential energy.
• Temperature is defined from kinetic energy.
• Solids have molecules at fixed positions vibrating.
• Liquids have molecules close together in random fashion, free to move.
• Gases have molecules separated moving at great speed.

Thermal Properties - Temperature

• Temperature measures kinetic energy associated with molecular motion.
• Defining temperature for a perfect vacuum isn't possible.
• Temperature is relevant for systems at thermal equilibrium.
• Absolute zero is approximately -273.15°C.
• Temperature units are Kelvin (K) or Celsius (°C).
• The formula to convert Celsius to Kelvin is TK = ToC + 273.15 K.

Temperature Scales and Zeroth Law

• The upper limit of the temperature scale at 1 atm is 100°C or 373 K.
• The lower limit of the temperature scale at 1 atm is 0°C or 273 K.
• The Zeroth Law of Thermodynamics states that if two objects are each in thermal equilibrium with a third object, they are also in thermal equilibrium with each other.

Thermal Properties - Gas Pressure

• Pressure is defined as Force per unit Area (P = F/A).
• For fluids including gases, Pressure = density of fluid * gravity * height (P = ρfluidgh).
• 1 atm is equivalent to 760 mmHg, which equals 10^5 Pa.
• 1 Torr is equivalent to 1 mmHg, which equals 133.3 Pa.

Gas Laws - Boyle's Law

• Boyle's Law, at constant temperature, states Pressure x Volume = constant, expressed as P x V = nRT
• "n" represents the number of moles of gas.
• "R" equals 8.3 J/(mol·K) as the Gas constant.
• T is temperature.

Measurement of Gas Pressure

• Spirometers/Spirograph are employed to determine flow volume by measuring lung capacity, and lung volume for diagnosing pulmonary fibrosis, asthma, and cystic fibrosis.
• Bourdon gauges are used to measure pressure.

Gas Solubility in Liquid

• A solution is a homogeneous mixture with 2+ components.
• A solute is the dissolved agent, less abundant in the solution.
• A solvent dissolves the solute, more abundant in the solution.
• A saturation solution has the maximum amount of solute at a defined temperature.

Gas Solubility, Pressure, and Temp

• Gas solubility in water increases proportionally with increasing pressure.
• Solubility of solid solutes in water increases with increasing temperature, but solubility of gases in water decreases with increasing temperature.
• Henry's Law describes the relationship between pressure and solubility.
• Henry's Law: C = kP or S = kP with "C or S" being the concentration of dissolved gas, "P" being the pressure of the gas, and "k" being a constant.

Osmosis and Osmotic Pressure

• Osmosis is the tendency of a fluid, usually water, to pass through a semipermeable membrane into a solution where the solvent concentration is lower and the solute concentration is higher.
• Equilibrium is reached when there is no longer water movement.
• Osmotic pressure (π) is the minimum pressure needed to prevent the inward flow of pure solvent across a semipermeable membrane.
• Osmotic pressure is defined as π = nRT/V, where "n" is moles of solution, "R" is the gas constant, "T" is temperature in Kelvin, and "V" is the volume of the solution in K.
• In hypertonic solutions, cells shrink.

Vapor Pressure

• Vapor pressure happens below atmospheric pressure.
• During evaporation vapor pressure is lower than atmospheric pressure
• During boiling vapor pressure equals atmospheric pressure
• Vapor pressure is the pressure exerted by a substance against the external pressure, usually atmospheric pressure.

Thermal Properties of Matter

• Amount of heat energy Q needed to produce temperature change of ΔT is given by: Q = c ⋅ m ⋅ ΔT.
• "c" is specific heat of a substance (J/kg·K).
• "m" is the mass of substance (kg).
• "ΔT" is defined as a change in temperature (K).
• Higher "c" means harder to change temperature.

Thermal Properties and Phase Change

• Heat of transformation, Qtransform = L ⋅ m, L: latent heat (J/kg).

Transference of Heat

• Conduction: Heat transfer through a material, the amount of heat depends on the temperature difference, cross-sectional area, and length of the material.
• Factors that affect transference of heat: time during conduction, the temperature difference between the ends of the bar, the cross sectional area and the length of the bar.
• Formula: H = (Q/t) = kA(TH - TC)/L, where k is thermal conductivity.
• Conductive heat is higher in concrete compared to gases.
• Convection: Energy transfer by the motion of a liquid or gas.
• Radiation: Energy transfer by Emission or absorption of electromagnetic waves.
• Stefan-Boltzmann constant is σ: 5.6705×10-8 W⋅m-2⋅K-4
• Radiated power P is per the formula P = eσAT^4

Entropy

• Entropy measures a system's disorder.
• Entropy increases with disorder.
• The most probable final or equilibrium state of a system will usually be the one that is the least ordered as it has higher entropy.
• Work is required to reduce entropy.
• In an irreversible process, entropy changes do not cancel and there is a net increase in entropy.
• In reversible processes with constant temperatures, ΔS = Q/T.
• In irreversible processes, thermal equilibrium is: ΔSnet = ΔShot + ΔScold.
• There is a natural tendency to lose order
• In the universe the sum of disorder is always increasing